The use of investment casting molding is well documented in the prior art. This technique is also referred to as the lost wax process. This type of molding technique is advantageous for delicate and complex component geometry fabrications such as dental prosthesis, miniaturization components and high performance components for aerospace and munitions where fastenings of complex geometries are not desirable.
The process of investment casting molding generally includes the steps of assembling wax preforms to a sprue, administering ceramic to the outside of the wax assemblage, inversion of the assemblage and heating to remove the wax leaving the desired cavity geometry, casting of molten metal into the righted mold cavity and destruction of the mold and finishing of the cast product components to remove sprue connections and casting defects.
Such an investment casting molding technique is set forth in U.S. Pat. No. 4,240,493 which also discloses at column 3, line 22, that the wax pattern material can be removed using a steam-fired autoclave, wherein steam is the appropriate agent for the heating, melting and thus removal of the wax from the mold cavity.
It is identified in U.S. Pat. No. 4,700,760 that in investment casting molding, temperatures may be as high as the range of 900.degree. to 1200.degree. F. to facilitate the melting out of wax or plastic preforms and their attendant sprue rods.
U.S. Pat. No. 4,777,996 describes the lost wax process wherein the disadvantages of wax pattern removal using traditional heating is set forth. At column 2, line 9 through 13, it is identified that burning out of wax from an investment cast molding creates environmental considerations due to the large amount of wax that is necessarily burned. Such burnout in addition to melting of the wax is necessary to insure complete removal of the wax, so as to avoid molding defects and mold cracking that occur when ensuing hot metal is poured into the investment casting mold.
In addition to the removal of pattern material, such as wax, by a melting operation, U.S. Pat. No. 4,691,754 identifies that some pattern material is gasified at destructive temperatures induced by the molten metal actually being introduced into the investment casting mold during casting. This technique suffers from control over the evolution of the gasified pattern material. Although the patent describes that the gas can be absorbed by the mold, in fact total gas dissipation is not complete without some possible molding defects such as porosity formation in casting which is considered a defect.
U.S. Pat. No. 4,651,799 is directed to investment casting molds and identifies at column 7, line 18 through 27, that in the autoclave where the wax is melted out of the mold, a significant differential in the appropriate temperature exists, such that the melting point of the wax is at approximately 160.degree. F., while the autoclave temperature is generally about 340.degree. F. Such high temperatures of a traditional autoclave induce problems in wax destruction, and mold cracking from the differential melting and expansion of the interiorly-contained wax prior to that portion of the wax located near the sprue orifice providing an outlet from the cavity in the mold.
U.S. Pat. No. 4,603,728 discloses the problem in the lost wax process, wherein varying temperatures are experienced during wax removal with attendant complications and damage to the mold. Such concerns are identified at column 2, line 21 through 28 of the patent.
U.S. Pat. No. 4,356,859 recounts the problem with melting out wax from an investment casting mold, wherein the wax expands and creates cracks and defects in the mold. It is identified that steam heat lessens the degree of mold defects introduced during the wax removal process. However, steam heat is limited in the temperatures to which it can be used and therefore, its flexibility in being matched with particular wax, resin, metal or plastic pattern material.
Various fluorocarbons are known in the prior art, such as those recited in U.S. Pat. No. 2,459,780 which describes the heat transfer capabilities of fully fluorinated and fully saturated carbon compounds.
These compounds are additionally disclosed in TETRAHYDRAN, 1963, volume 19, page 1893 through 1899 and an article entitled "Polycyclic Fluoroaromatic Compounds III", Harrison, et al.
The use of heating solder for vapor phase soldering using fluorocarbons has been disclosed in U.K. patent application No. GP 2110204A.
Additional fluorocarbons useful for vapor phase soldering are identified in U.K. patent application No. GP 2194231A.
The use of perfluorotetradecahydrophenanthrene has been set forth in U.S. Pat. No. 4,549,686.
The present invention overcomes the difficulties in appropriate heating of specific melting point waxes, resins or plastics and the uniform application of heat to intricate investment casting molds as set forth below.